Zapping Tiny Metal Drops With Sound Creates Wires for Soft Electronics

janrinok writes:

A new way to make stretchy wiring uses ultrasound and microscopic spheres of liquid metal

Zapping liquid metal droplets with ultrasound offers a new way to make wiring for stretchy, bendy electronics.

The technique, described in the Nov. 11 Science, adds a new approach to the toolbox for researchers developing circuitry for medical sensors that attach to the skin, wearable electronics and other applications where rigid circuit electronics are less than ideal.

The researchers began by drawing on sheets of stretchy plastic with lines of microscopic droplets made of an alloy of gallium and indium. The metal alloy is liquid at temperatures above about 16 Celsius.

Though the liquid metal is electrically conductive, the droplets quickly oxidize. That process covers each of them with a thin insulating layer. The layers carry static charges that push the drops apart, making them useless for connecting the LEDs, microchips and other components in electronic circuitry.

By hitting the microspheres with high-frequency sound waves, the researchers caused the microscopic balls to shed even smaller, nanoscopic balls of liquid metal. The tiny spheres bridge the gaps between the larger ones, and that close contact allows electrons to tunnel through the oxide layers so that the droplets can carry electricity.

When the plastic that the drops are printed on is stretched or bent, the larger balls of metal can deform, while the smaller ones act like rigid particles that shift around to maintain contact.

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